One pack-year equals smoking one pack (20 cigarettes) per day for one year. It is the standard clinical unit for quantifying lifetime tobacco exposure.

Who qualifies for lung cancer screening?

Current USPSTF guidelines (2021) recommend annual low-dose CT screening for adults aged 50–80 who have a 20 pack-year history and currently smoke or quit within the past 15 years. Always confirm with your clinician.

Does stopping smoking reduce my pack-year count?

No — pack-years reflect cumulative lifetime exposure and do not decrease after quitting. However, quitting does substantially reduce future cancer and cardiovascular risk.

How do I calculate pack-years for cigars or pipes?

This tool is designed for cigarettes. For other tobacco products, consult your clinician for an equivalent conversion, as there is no universally accepted standard formula.

Is this tool a medical diagnosis?

No. This is an educational calculator only. Consult a qualified healthcare provider for medical advice, screening decisions, and risk assessment.

Does it matter how long ago I quit?

Under the USPSTF 2021 recommendation, yes: screening applies if you still smoke or quit within the past 15 years. The American Cancer Society's 2023 guideline drops the years-since-quitting limit and recommends yearly screening at age 50 to 80 with 20 or more pack years, whenever you quit.

How do I count pack years if my smoking changed over time?

Work out each period separately and add them. One pack a day for 10 years (10) plus half a pack a day for 20 years (10) is 20 pack years. If the periods are hard to separate, enter your average cigarettes per day.

Pack Year Calculator

Calculate your smoking history in pack-years (packs per day × years smoked) for clinical lung cancer risk assessment.

Pack years = cigarettes per day ÷ 20 × years smoked.

Smoking History

Enter your average daily cigarette count and years smoked.

Cigarettes per day

cigs/day

One pack = 20 cigarettes.

Years smoked

years

Result

Enter your smoking history and click Calculate.

Quick answer

Pack years = cigarettes per day ÷ 20 × years smoked. One pack a day for 20 years, or two packs a day for 10 years, is 20 pack years. That is the threshold USPSTF uses, together with age 50 to 80, for yearly low-dose CT lung cancer screening.

Examples

Smoking history	Pack years
20 cigarettes a day for 20 years	20
40 a day for 10 years	20
30 a day for 15 years	22.5
10 a day for 30 years	15
5 a day for 40 years	10

Enter cigarettes per day and years.

Summary

A pack-year is a standardized clinical unit that quantifies cumulative tobacco exposure. It is calculated by multiplying the average number of cigarette packs smoked per day by the total number of years smoked. Clinicians use this figure to assess lung cancer screening eligibility (e.g., USPSTF criteria) and to stratify COPD, cardiovascular, and surgical risk.

How it works

Enter the average number of cigarettes you smoke (or smoked) per day.
Enter the total number of years you have smoked.
The calculator divides cigarettes per day by 20 to get packs per day.
Packs per day is multiplied by years smoked to produce the pack-year total.
A risk summary based on common clinical thresholds is displayed.
Use the result in conversations with your healthcare provider.

Use cases

Determine eligibility for annual low-dose CT lung cancer screening.
Document smoking history for surgical pre-assessment.
Stratify COPD and cardiovascular risk in primary care.
Support pulmonology referrals requiring a quantified smoking history.
Patient education — visualize cumulative tobacco exposure.
Research and clinical trial enrollment screening.

Frequently Asked Questions

Last updated: 2026-05-28 · Reviewed by Nham Vu